Since the development of the integrated circuit (IC), the semiconductor industry has sought to continue to improve the performance or size of the IC. Many of these improvements have focused on smaller feature sizes so that the speed of the IC can be increased. By decreasing the feature sizes, the density of devices (e.g., transistors, diodes, resistors, capacitors, etc.) on the IC has increased. By increasing the density, distances between devices generally decreases, which allows for a smaller resistance and capacitance between devices. Thus, a resistance-capacitance (RC) time constant can be decreased.
With the decrease in distances between devices generally comes more difficulty in ensuring proper alignment of features, such as contacts, in overlying layers with features in an underlying substrate, such as a source or drain. Tolerances can become very small in smaller technology nodes, and a small amount of misalignment of an overlying layer can cause overlay problems that can render devices faulty.
Further, features in devices that are intended to prevent faults in the case of misalignment can become thinner and weaker in smaller technology nodes. These thinner layers may not be able to withstand an etchant that is not selective to the layers. Even further, these features can be exposed to multiple etchants from various sides, particularly in the developing gate-last processes that are now being developed. The attacks on these features by the etchants can cause a subsequent unintended short circuit between conductive features, which can render devices useless.